1. Field of the Invention
The present invention relates to a surface acoustic wave device, more particularly to a surface acoustic wave device in which a transducer is arranged on a plane surface of a substrate.
2. Description of Related Art
A typical surface acoustic wave device (SAW device) includes a substrate, an interdigital transducer (IDT), and another IDT or a reflector. The IDT and the reflector are formed on a substrate. The IDT generates or receives a surface acoustic wave on the substrate. The reflector reflects the surface acoustic wave.
A typical IDT has an interdigital shape (comb shape), and includes digital parts (finger-like parts) with a straight line shape. JP-2005-111471A corresponding to US-2005/0083785A discloses a SAW device in which an IDT is composed of straight line parts or circular arc parts.
In a plane type SAW device, an IDT is formed on a plane surface of a substrate. A conventional plane type SAW device thus has a problem of diffracting a surface acoustic wave and dissipating the energy of surface acoustic wave. To address this problem, JP-2002-26688A discloses a spherical type SAW device in which an IDT is formed on a spherical surface of a spherical substrate.
A reason of occurrence of the diffraction in a conventional plane type SAW device is that an IDT or a reflector has ends because of its straight line shape or circular arc shape. In a conventional plane type SAW device, a surface acoustic wave generated by an IDT is escaped from a space between the IDT and the reflector or between the IDT and the IDT due to the diffraction. A conventional plane type SAW device cannot efficiently use all of the surface acoustic wave energy generated by the IDT.
A technique described in JP-2002-26688A may suppress the diffraction by placing an electrode on the spherical surface. However, the technique described in JP-2002-26688A cannot be applied to a plane type SAW device to suppress the diffraction, because an electrode of the plane type SAW device is located on the plane surface of the substrate.